Linear actuators are mechanical devices which are used to perform repetitive actions requiring linear motion. For example, linear actuators can be used in an assembly plant for placing caps on bottles, for automatically stamping or labeling mail, for glass cutting, for placing electronic components on printed circuit boards, for testing various buttons or touch areas on electronic devices, for automation, and for a wide variety of other purposes as well.
In plants designed to assemble electronic devices, actuators are used to, for example, pick up and move components provided by a parts feeder or similar apparatus. In modern printed circuit board assembly lines, the center points of the smallest parts feeder stations are separated by a distance, or pitch, of slightly less than 8 mm. Thus, in order for two actuators to be paired with two adjacent part feeder stations arranged at an 8 mm pitch, each of the actuators must have a diameter of less than 8 mm in order to enable components to be retrieved from the adjacent parts feeders and properly placed upon on circuit boards.
Typically, enterprises involved in the electronic assembly of devices comprised of small parts utilize pneumatic actuators, or “slides”, to manipulate such parts. Although pneumatic slides are generally inexpensive, the component parts used in, for example, various electronic or industrial devices can be so small and fragile that compressed air pneumatic slides may cause damage when placing such parts on a circuit board due to the friction forces that must be overcome to achieve actuation in typical compressed air pneumatic slides. Further, pneumatic slides are known to have a somewhat limited lifetime, and may sometimes last less than 10M cycles.
In contrast, magnetic actuators typically enjoy a longer lifetime than pneumatic slides. In addition, magnetic actuators can be designed to “soft-land” and control the applied force, thereby reducing the risk of part breakage. Examples of such actuators can be found in U.S. Pat. No. 5,952,589 entitled “Soft Landing Method For Probe Assembly,” assigned to the assignee of the present application and incorporated by reference herein in its entirety. However, magnetic actuators can be expensive to manufacture.